The invention relates to height adjustment mechanisms for work surfaces, such as table tops.
It is known to provide a height adjustment mechanism for a work surface including a counterbalance mechanism for providing a counterbalance force opposing a downward force including tending to lower the work surface, a brake mechanism for releasably retaining the work surface in a desired vertical position, and a manual operated release mechanism for selectively releasing the brake mechanism to permit vertical movement of the work surface, as evidenced by U.S. Pat. Nos. 2,892,050; 3,213,809; and 5,797,331. Further, it is known to provide means for preventing release of the work surface for vertical movement when the counterbalance force and the downward force are out of balance, as evidenced by U.S. Pat. No 5,706,739 and commonly assigned U.S. application Ser. No. 09/215,838.
The present invention is generally directed towards a height adjustment mechanism for a work surface and more particulars to a mechanism employing a brake mechanism for releasably retaining the work surface in a desired vertical position and a manual operator for selectively releasing the brake mechanism, except when a vertically downwardly directed force acting on the work surface differs by some given amount from a counterbalance force tending to oppose downward movement of the work surface.
More specifically, the present invention is directed towards an improved interlock mechanism particularly adapted to be used with a counterbalance table mechanism of the type described in U.S. Pat. No. 5,797,331, wherein release of the brake mechanism is prevented when the force exerted by a counterbalance mechanism on the work. surface differs by some given extent from a downwardly directed force acting on such work surface.
In accordance with the present invention, the interlock mechanism includes an interlock plate pivotally supported by the base or frame of a table mechanism to undergo movement between fist and second blocking positions when the counterbalance force is less than and greater than the downward force, respectively, through a neutral position, wherein the force essentially corresponds to the downward force, and the brake mechanism is freed for release by a user.